Comparison of Signal-to-Noise Ratio at 3T MRI of the Prostate: The Influence of Endorectal Coil and Body Habitus

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Abstract

BACKGROUND: Prostate gland cancer is the second most common cause of death from cancer among men. Multiparametric MR imaging, currently the most accurate imaging technique for prostate cancer detection and staging, utilizes an endorectal coil (ERC) to improve image duality. While some practitioners have transitioned to imaging protocols without endorectal coil due to patient discomfort, invasiveness and cost, there is insufficient data to support that one approach is superior or equivalent to the other. Thus, we propose an objective step-wise determination of signal-to-noise ratio (SNR) gains attributable to the endorectal coil in a 58 patient cohort of. This will provide data to guide the optimization of non-endorectal coil MR imaging protocols in patients with suspected prostate cancer.
METHODS: To assess the impact of SNR on the performance of two different non-ERC protocols, patients were randomized into 1 of 2 arms: a standard non-ERC protocol (T2 and DWI) and enhanced non-ERC protocol with twice as many signal averages. Patient subsequently underwent the standard clinical ERC protocol. Body habitus information was used to determine if decreases in SNR could be attributed to increase body fat and subsequently, increased distance from the prostate to the surface coil in the non-ERC protocol, and whether this could be corrected with an ERC protocol. SNR was calculated using regions of interest {ROIs) were drawn in the anterior and peripheral zones at the mid-prostate level, using homogeneity in urine as a benchmark for noise.
RESULTS: The mean SNR measurements for T2W images with ERC were twice as large as mean SNR measurements for T2W images without ERC. Similarly, we were able to demonstrate a 1.7x increase in SNR on diffusion weighted images with ERC at b = 0. In addition ANOVA tests verified our hypothesis that the endorectal coil significantly (p < 0.05) improves SNR over either non-ERC methods, and no significant differences in SNR were detected between the non-ERC images and "enhanced" ERC images for both T2W and DWI at b = 0. Comparisons between SNR and body habitus information, specifically BMI, waist circumference, and anterior-posterior distance from anterior-to-prostate and prostate-to-rectal wall in showed no significant difference in both T2W and DWI, b = 0 images between either set of protocols. This information can further guide recommendations for multiparametric MR imaging of the prostate with or without endorectal coil, though more data is required to guide coil placement in obese vs thin individuals.